1. Field of the Invention
The present invention relates to a power supply apparatus and an image forming apparatus mounting the same.
2. Description of the Related Art
Japanese Patent Application Laid-Open No. 2000-102249 discloses a configuration of a high voltage power supply for use in an image forming apparatus using an electrophotographic system.
The above high voltage power supply can be mounted on the image forming apparatus to generate a high bias voltage for use in each step of the electrophotographic process. For example, four high voltage power supplies are mounted on a 4-color image forming apparatus, and the output voltage of each high voltage power supply can be used as a bias voltage of yellow, cyan, magenta and black in a charging step or a developing step respectively.
However, in order to provide a plurality of kinds of high bias voltage, the above conventional techniques need the same number of voltage rising circuits as the kinds of high bias voltage. That is, the number of high voltage power supplies to be mounted on the image forming apparatus increases proportionally with the number of kinds of high bias voltage, leading to an increase in costs of the image forming apparatus.
In order to suppress the increase in costs, there has been proposed a configuration of sharing a transformer used by each high voltage power supply with a plurality of high voltage power supplies. However, the configuration is required to consider the characteristic variations of a target voltage of each high voltage power supply, a voltage rising transformer and the like to determine the output level of the shared transformer power supply. Therefore, it is difficult to perform optimization according to the operating conditions of each high voltage power supply and thus a ripple voltage occurring in the output voltage may increase.